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A Structural Interpretation Of The Goodwyn South/Tidepole Area, Rankin Platform, North West Shelf, Western Australia.

Clark, Victoria

Honours Degree, 1990

University of Adelaide

Abstract

The Goodwyn South/Tidepole area, situated along the eastern margin of the Rankin Platform, lies in a province known for its large accumulations of natural gas and condensate with minor oil. The Rankin Platform forms the eastern culmination of the Exmouth Plateau, which was created by asymmetrical continental extension and breakup in the Early to Mid Jurassic. Structures imaged by the Goodwyn South/Tidepole 3-D seismic survey were formed in response to the continental rifting episode.

Five main faults which bound a series of blocks are recognised in the study area. Four are discussed in detail. Prior to the main period of extension, movement began along the Tidepole and probably also the Goodwyn South-bounding Fault in the Late Triassic. It caused a compactional growth syncline and rollover anticline in the Tidepole Fault hanging wall sediments, and a small amount of sediment thickening in the Goodwyn South-bounding Fault hanging wall.

The major period of rifting began in the Sinemurian, when activity commenced on the Goodwyn West-bounding Fault, and the Goodwyn Block was rotated northwards. Consequently, the Goodwyn South-bounding Fault would have been forced to rotate to the north also, necessarily creating a graben at the palaeosurface. The upper hanging wall sediments were deposited into the graben as a broad rollover anticline complicated by a crestal collapse graben, which is defined by antithetic and synthetic faults.

After continental breakup, Jurassic sediments were deposited into the Barrow-Dampier Sub-basin, onlapping onto the Rankin Escarpment. Loading may have caused the southward downwarping of the Goodwyn South/Pueblo sequence seen in the southern part of the block. Movement on the Sub-Jurassic Fault, which is a steep fault entirely buried by the Barrow-Dampier Sub-Basin and which may be the "branch to detachment" suggested by some authors, ceased at or before the end of the Jurassic.

Horizon attribute data have been employed in this structural interpretation, and have served to accurately define the positions of faults observed on seismic sections, and to delineate small lineations which may otherwise go unnoticed.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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